1. Field of the Invention
The present invention relates to a method of converting the format of encoded video data and an apparatus therefor, which convert a bit stream of a given encoded video data format into a bit stream of another encoded video data format.
2. Description of the Related Art
With rapid advances in video processing techniques, it has become common to, for example, distribute, view, save, and edit moving picture (video) data as digital data. Recently, services which allow users to view digital videos with portable terminals are being put into practice as well as handling digital videos by using video equipment and computers.
With regard to video transceiving methods, video data are exchanged through various media such as cable TVs, the Internet, and mobile telephones in addition to ground-based broadcasting and satellite broadcasting. Various-video encoding schemes have been proposed in accordance with the application purposes of videos and video transfer methods.
As video encoding schemes, for example, MPEG1, MPEG2, and MPEG4, which are international standard schemes, have been used. These video encoding schemes differ in their picture sizes and bit rates suitable for their data formats (encoded video data formats). For this reason, in using videos, encoded video data formats complying with video encoding schemes suitable for the purses and transfer methods must be selected.
As handling of videos as digital data has become common practice, demands have arisen for using a video stored in a given encoded video data format with a medium or application purpose different from the original medium or application purpose. When, for example, the bit stream of encoded video data stored in a data format based on MPEG2 is to be used with a portable terminal, the MPEG2 encoded video data must be converted into a bit stream in another encoded video data format, e.g., an encoded video data format based on MPEG4, upon changing encoding parameters such as the encoding scheme, picture size, frame rate, and bit rate because of the limitations imposed on display equipment and associated with channel speed.
As a technique of format-converting (transcoding) a bit stream between different video encoding schemes, a format conversion technique based on re-encoding is known, which decodes a bit stream as a conversion source first, and then encoding the decoded data in accordance with an encoded video data format as a conversion destination.
In the above format conversion technique for encoded video data, which is based on the conventional re-encoding scheme, encoding parameters for the conversion destination must be determined before format conversion. For this reason, the parameters cannot be changed in accordance with the situation during processing. It is therefore difficult to estimate the overall processing quantity. In order to perform format conversion simultaneously with viewing of an original video or converted video or perform format conversion in accordance with the transmission speed in streaming transmission, the user must determine appropriate encoding parameter by trial and error. In addition, since the picture quality of a video generated by format conversion cannot be known until the end of processing, if the picture quality is insufficient, conversion processing must be redone from the beginning.
In addition, the conventional format conversion technique for encoded video data allows only conversion of the entire interval of a given series of videos into another series of videos. When, therefore, a bit stream in a given encoded video data format is converted into bit streams in a plurality of encoded video data formats in order to simultaneously transmit the bit streams from many media, decoding, video data conversion, and encoding must be performed a plurality of times in accordance with the plurality of encoded video data formats as conversion destinations. This processing takes much time.
Furthermore, there are many demands for a technique of generating a digest by extracting only desired portions from a plurality of videos and performing format conversion and a technique of performing format conversion upon erasing unnecessary portions. In order to realize such techniques by the conventional format conversion methods, editing such as partial extraction and partial erasure must be independently performed before or after format conversion, resulting in poor efficiency.
It is an object of the present invention to provide a method of converting the format of encoded video data and an apparatus therefor, which can automatically change processing parameters at the time of format conversion.